Destroyed R888 - Too Low Pressure?

[MrStabby]

R888s cold at 22psi all round. A warm up lap or two then destroyed one of the tyres as i started to push a little. The instructors said that the tyre failed because 22psi is too low and I probably pulled one side off the rim. Said I need start on at 26psi, heat them up, then bleed back to the desired hot pressure. Is that a thing? I haven't heard of it before.

[niZmO_Man]

Not much of a reply, but I've read the R888s aren't great for heavy cars. Also 22psi seems quite low.

[sav man]

I was starting my tyres (Dunlop's) at 22psi cold at Phillip Island a few weeks ago, and I didn't have any problems

[djr81]

  On 09/12/2015 at 11:09 PM, MrStabby said:

R888s cold at 22psi all round. A warm up lap or two then destroyed one of the tyres as i started to push a little. The instructors said that the tyre failed because 22psi is too low and I probably pulled one side off the rim. Said I need start on at 26psi, heat them up, then bleed back to the desired hot pressure. Is that a thing? I haven't heard of it before.

What was left of the thing by the time you pulled up/got back? Yes it is possible (Although Id reckon unlikely) to pull the bead off the rim if you went really hard on low pressure and hit a kerb etc. Maybe warm them up at a slower rate would be better. The other way works too but is a lot of stuffing around.

But all up it sounds unlikely. The things were stretched on the rims I trust?

[MrStabby]

They are 255/35 on R34 GTR 9 inch rims, which is my old track setup. I was going to use them until they wore out and then put something like Hankook RS-3s on for street.

Here's what was left

[Duncan]

well, 22 definitely isn't too low for a starting pressure, but like djr said you might have been unlucky while warming up, especially since it failed immediately. It's easy to add 10psi to a tyre on a heavy car once it is working hard

I'd ask toyo in this case.

[V28VX37]

For heavy cars (1400kg+) Toyo recommend 27-35psi cold for the R888 here: http://www.toyo.co.uk/page/index/identifier/set-up-advice

I'm definitely no expert but 22psi does sound pretty low on a GT-R.

[Duncan]

Very interesting, thanks for posting that up. The Kumho v70s like very high pressures (45ish) as well.

I have to say though, there is a huge leap in target pressure between a 1000 and 1400kg car, and while I don't know more than the manufacturer I wonder if they recommend that high because they tyres can fail otherwise (at the cost of performance, as many have pointed out about these tyres on a skyline...)

The other thing that table tells us is 17psi is not too low for a starting pressure....

[MrStabby]

Well there you go - thanks V28.

And i was thinking that 30-32 hot was what i should be aiming for. I think i'm going to have to get something to check hot temperature across the tread and work it out for myself.

[MrStabby]

Response from Toyo - no clear answer to this, which is good in a way - I don't feel like an idiot anymore.

"Hi Adam,

What sort of failure?
It sounds like the failure was casing disintegration?

22psi cold is good, 30hot hot is spot on
Assuming you checked the pressures that day and the failure was casing disintegration, the only logical cause is a puncture.

Regards,



Steven Burke

Tyre Technical Manager | Toyo Tyre & Rubber Australia Limited"

[djr81]

Puncture is the next obvious cause. Have seen tyres destroyed after a puncture and that is what they look like.

[Duncan]

Good on Toyo for answering so swiftly.

But I'd wonder how a puncture occurred, they aren't really that common on tracks (common enough off tracks )

[Kinks]

  On 10/12/2015 at 9:22 PM, Duncan said:

The other thing that table tells us is 17psi is not too low for a starting pressure....

Not for an 800kg car. But an 800kg car will cause much less sidewall flex and much less heat generated in the canvas of the tyre. Do the same thing in a 1600kg tyre and you will be rolling around on the sidewalls.

Probably better to err on the side of caution and start with a slightly higher cold pressure and bleed air to maintain target hot pressure.